The last great primary forests of Russia's Far East are known for their tigers and bears, but they are also the domain of giant owls. A new study finds that the health of the rare Blakiston’s fish owl is intrinsic to that of these northern forests. The birds rely on old-growth forests along streams for both breeding and to support healthy populations of their favorite prey: salmon.

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Large trees provide breeding cavities for the enormous bird, which has a 6-foot wingspan. When these massive trees die and topple into streams, they disrupt water flow, forcing the gushing river around, over, and under these new obstacles. The result is stream channel complexity: a combination of deep, slow-moving backwaters and shallow, fast-moving channels that provide important microhabitats critical to salmon in different developmental stages.

The study, led by WCS and the University of Minnesota, appears in the journal Oryx. The authors studied the foraging and nesting characteristics of Blakiston’s fish owl in Primorye, Russia, where they looked at nesting habitat over 7,804 square miles. They found that large old trees and riparian old-growth forest were the primary distinguishing characteristics of both nest and foraging sites.

The authors say that management and conservation of old-growth forests is essential for sustaining this species because they are central to the owls' nesting and foraging behavior. Moreover, conservation of Primorye's forests and rivers sustains habitat for many other species: including eight salmon and trout species that spawn there; some of the 12 other owl species found in Primorye; and mammals like the endangered Amur (or Siberian) tiger, Asiatic black bear, and wild boar. Listed as Endangered by IUCN, Blakiston's fish owl is restricted to riparian areas in Russia, China, Japan, and possibly North Korea.